Thermal conductor

ABSTRACT

The invention relates to an exhaust-gas thermal conductor ( 1 ), comprising a tube array with exhaust gas flowing therethrough and cooling medium flowing around the same. The tube array is welded to a tube base ( 5 ), connected to the housing ( 2 ). As a result of varying temperature effects on the tubes and on the housing ( 2 ) whilst operating the exhaust gas thermal conductor ( 1 ), thermal stresses, as a result of differing expansion of the tubes and the housing ( 2 ), occur. According to the invention, said stresses may be avoided, whereby slots ( 8 - 10 ) are arranged in the housing sleeve ( 2 ), which are externally sealed by means of a bellows.

The invention relates to a heat exchanger, in particular an exhaust gasheat exchanger, heat exchanger, having a fluid channel, such as a tubeor multiplicity of tubes, like a tube array, through which a firstmedium, such as exhaust gas, can flow, and a second fluid channel, suchas a housing, through which a second medium, such as a coolant, canflow, the ends of the tube array being connected to the tube plates, forexample in a cohesive manner, and the tube plates being connected to thehousing, for example in a cohesive manner.

Such a heat exchanger as an exhaust gas heat exchanger has beendisclosed by DE-A 199 07 163 from the applicant. In this known design,the ends of a tube array are accommodated in appropriate openings in atube plate and are welded to the tube plate. The tube array with the twotube plates is arranged in the housing, the tube plates being weldedcircumferentially to the shell of the housing. Thus, the tubes arefirmly connected to the housing via the tube plate, which can lead tothermal stresses under certain conditions. Hot exhaust gas flows throughthe tubes on the inside and colder coolant flows on the outside and alsowashes around the inside of the housing. In particular in the case ofrelatively long tube lengths of such an exhaust gas heat exchanger, forexample for commercial vehicles, the different expansions of tubes andhousing shell can lead to stresses which are no longer permissible,which can result, for example, in destruction of the tube-plateconnection.

It is therefore an object of the invention to improve an exhaust gasheat exchanger of the type mentioned at the beginning to the effect thatthermal stresses on account of different expansions are reduced oravoided, so that the heat exchanger achieves the service life which isnormal in motor vehicles.

This object is achieved by the features of patent claim 1.

In a heat exchanger, such as in particular an exhaust gas heatexchanger, having a fluid channel, such as a tube array, through which afirst medium, such as exhaust gas, can flow, and a second fluid channel,such as a housing, through which a second medium, such as a coolant, canflow, the ends of the tube array being connected to the tube plates, forexample in a cohesive manner, and the tube plates being connected to thehousing, for example in a cohesive manner, the object is preferablyachieved by the housing having an expansion element.

It is expedient in this case if a sealing element, such as a metalbellows, is arranged on the housing, covering and sealing the expansionelement.

It can also be advantageous if the expansion element is formed in onepiece with a sealing element.

Furthermore, it is expedient if the expansion element is formed as acircumferential bead.

It is particularly advantageous, moreover, if a sealing element, such asa metal bellows or another sealing element, for example made of plasticor an elastomer, is arranged on the housing, covering and sealing theexpansion element.

The expansion element can also be formed in one piece with the sealingelement, for example as a circumferential bead, which performs thesealing function and the expansion function at the same time.

It is advantageous in this case if the expansion element is at least oneregion of the housing that is provided with slots. It is expedient inthis case if, as an expansion element, the housing or a region of thehousing has slots which run transversely with respect to thelongitudinal direction of the tubes and in the circumferential directionof the housing, which in each case extend only over part of thecircumference and which in the circumferential direction partly overlapslots arranged offset axially.

In this case, in one exemplary embodiment, it can be expedient if atleast one group of slots having at least two slots is provided in thehousing. It is advantageous if the at least one group of slots isarranged in a central region of the housing, as viewed in thelongitudinal direction of the heat exchanger. It is also advantageous ifthe at least one group of slots is arranged in an end region or close toan end region of the housing, as viewed in the longitudinal direction ofthe heat exchanger.

In a further exemplary embodiment, it is advantageous if two groups ofslots are provided. In this case, it can be advantageous if the twogroups of slots are arranged in the two end regions or close to the endregions of the housing. Likewise, it can be expedient if the groups ofslots has at least two or a multiplicity of slots, such as three, four,five, six, etc. slots.

According to a further idea of the invention, it can be expedient iffour slots are arranged in the housing or in a group of slots, in eachcase two extending over less than half the circumference in one of twotransverse planes and slotted regions of the other transverse planebeing located opposite the non-slotted regions of a transverse plane.

According to the invention, in a further exemplary embodiment it isexpedient if, given an arrangement of two slots per group of slots, theslots are spaced apart and are formed in such a way that they run besideone another in a subregion of their extent and leave a narrow landbetween themselves.

In a further embodiment of the invention, it is expedient if, given anarrangement of three slots per group of slots, the slots are spacedapart and are formed in such a way that they run beside one another in asubregion of their extent and leave two narrow lands between themselves.

It can also be expedient if, given a group of slots, at least two landsor a multiplicity of lands, such as three, four, etc., are formed, asviewed over the circumference of the housing.

It is likewise advantageous if, given a group of slots with anarrangement of two lands per group, the lands lie opposite one another,as viewed in the radial direction of the housing.

Moreover, it is expedient if, given a group of slots with an arrangementof two or more lands per group, the lands are distributed uniformly, asviewed in the circumferential direction of the housing.

It is advantageous if four lands are formed by four slots which partlyintersect at four points of the housing, that is to say that in eachcase two slots partly intersect in a region and thus form the land.

It is expedient if four times two parallel lands are formed by six slotswhich partly intersect at four points of the housing.

It is also expedient if the slots have a teardrop shape in their endregions.

Moreover, it is expedient if the slots are introduced into the housingby means of one of the following processes: laser cutting, water jetcutting, sawing, milling, erosion or punching.

It is also advantageous if the expansion element and/or the sealingelement is formed from one of the following materials: metal, steel,elastomer, silicone.

Likewise, it is expedient if the expansion element and/or the sealingelement is connected to a housing part or two housing parts or is formedin one piece with the latter.

According to the invention, it is expedient if the expansion elementand/or the sealing element is connected to the housing by welding,soldering, by means of clamping elements or by means of adhesivebonding.

If, in the case of such an exhaust gas heat exchanger, differentialexpansion occurs between the exhaust gas tubes and the housing shell,then, on account of the slots running transversely with respect to thelongitudinal direction of the tubes, the housing is capable of expandingin the same way as the tubes. This takes place as a result of elasticdeformation of the housing shell in the region of the slots, moreprecisely between two axially offset slots. In order that the coolantwhich washes around the tubes does not emerge into the open from theslots in the housing, a metal bellows is arranged on the housing overthe region of the slots, ensuring the necessary sealing and at the sametime being able to follow the expansions of the housing. On account ofthese measures, thermal stresses and component damage or destructioncaused by them are avoided, even in the case of long heat exchangerlengths.

An exemplary embodiment of the invention is illustrated in the drawingand will be described in more detail in the following text. In thedrawing:

FIG. 1 shows a perspective view of part of an exhaust gas heatexchanger,

FIG. 2 shows a plan view of part of an exhaust gas heat exchanger,

FIG. 3 shows a side view of the part of the exhaust gas heat exchangeraccording to FIG. 2 and

FIG. 4 shows a view of part of the exhaust gas heat exchanger with metalbellows,

FIG. 5 shows an extract of a heat exchanger,

FIGS. 6 a to 6 c show a view of arrangements of slots and lands, and

FIG. 7 shows a partial view of a heat exchanger.

FIG. 1 shows a perspective view of part of a heat exchanger, such as inparticular an exhaust gas heat exchanger 1, having a housing shell 2which is approximately rectangular in cross section and which, in itsend region 3, is somewhat enlarged in cross section. However, the crosssection can also have another geometry, such as round, polygonal,octagonal etc. The end 4 reveals the tube plate 5 with rectangularopenings to accommodate fluid channels, such as exhaust gas tubes, whichare not illustrated. The ends of these exhaust gas tubes are—asdescribed, for example, in DE-A 199 07 163 already mentioned—welded tothe tube plate which, in turn, is welded circumferentially to thehousing shell 3. Provided in the housing region 3 is an opening 7 forthe inlet of coolant, which is distributed in the interior of thehousing region 3 in an annular channel, not illustrated, and from thereflows through the heat exchanger on the outer side of the exhaust gastubes. Finally, approximately in the transition region of the housingregions 2 and 3, three slots 8, 9 and 10 running in the circumferentialdirection of the housing can be seen, the slot 10 being offset axiallywith respect to the two slots 8 and 9 and likewise being offset in thecircumferential direction.

FIG. 2 shows these slots 9 and 10 in a plan view of the housing 2/3 ofthe heat exchanger 1. The slots 9 and 10 extend in the direction of thecircumference of the housing as far as a circular or teardrop-shapedopening 11 or 12, respectively, which is intended to avoid notchstresses in this region. The slot 9 reaches as far as the outer edge 13,and the slot 10 as far as the outer edge 14.

As can be seen in FIG. 3, the slot 9 runs onward in the circumferentialdirection from the edge 13 as far as the circular hole 15, and the slot10 runs onward from the edge 14 as far as the circular hole 16. Bothslots 9 and 10 are offset axially approximately by a region of a few mm,for example 5 mm. The tube plate is indicated at the front end of thehousing 3 by a dashed line 5. The entire exhaust gas heat exchanger 1 isillustrated incompletely in FIGS. 1, 2 and 3, inasmuch as a seal for theslots 9 and 10 with respect to the outside is missing—this seal, in theform of a metal bellows, will be described in FIG. 4.

FIG. 4 shows a view of part of the heat exchanger with the two housingregions 2 and 3, a metal bellows 20 being arranged between these tworegions—said bellows covers the slots, which cannot be seen in thisdepiction, as have been described in the previous FIGS. 1 to 3. Themetal bellows is matched to the cross section of the housing 2/3 andtightly connected to the latter via its circumferential edges 21 and 22.As a result, coolant can no longer emerge to the outside from theinterior of the housing via the slots—at the same time this metalbellows 20 is able to compensate for the expansions of the two housingregions 2 and 3.

FIG. 5 shows a part of a heat exchanger 100 in which four slots 110 to113 are introduced into the wall 101 of the housing, the slots beingoffset axially and in the circumferential direction in such a way thatlands, which act as expanding or bending beams, remain between theslots.

As a result, one part of the heat exchanger can expand in such a waythat the housing shell of the heat exchanger is flexible as a result ofthe bending beam or beams and ensures expansion of the housing.

As shown in FIG. 5, two bending beams are formed by the lands 120 to 123for each face of the housing, this being the case on all four faces,that is to say even on the faces which cannot be seen in this view.

FIGS. 6 a to 6 c show variants of designs of slots and lands which aremachined into the housing shell in order to form the bending beams.

In FIG. 6 a, two slots 150, 151 are formed or introduced into thehousing. Between the slots there is a land 153, which serves as abending beam. Provided at the ends of the slots are teardrop-shapedcutouts. In FIG. 6 b, two slots 160, 161, 162 are formed or introducedinto the housing. Provided between these slots are two lands 163 and164, which serve as bending beams. Teardrop-shaped cutouts are providedat the ends of the slots.

The configuration of the slots of FIG. 6 c corresponds substantially tothe configuration of FIG. 6 b, the slots being angled over in a region170, 171. These regions can also be curved.

FIG. 7 shows a partial view of a heat exchanger 200 with fluid channelsthrough which a first medium can flow. In the exemplary embodiment of anexhaust gas heat exchanger, these are the fluid channels through whichthe exhaust gas flows.

A second medium can flow between the fluid channels 201 and possiblyaround the latter as a further fluid channel, in order to cool themedium in the first fluid channel. This second fluid channel istherefore located within the housing 202.

For the purpose of improved mechanical decoupling on account of thedifferent thermal expansion of the walls of the channels 201 and thehousing 202, a circumferential bead 210 is introduced into the housingat at least one point. As a result, the housing, which is generally at alower temperature than the inner channels during the operation of theheat exchanger, is able to expand when the inner channels expand onaccount of the thermal expansion, without destruction of the heatexchanger occurring.

The bead 210 is in this case constituted, for example, by a semicircularbulge. However, it can also have another form, such as in a folded ormeandering configuration. The bead can also be bulged inward, that is tosay formed as an indentation. During the formation of the bead, it isexpedient for the latter to be able to fulfill both expansioncharacteristics and sealing characteristics.

1. A heat exchanger, such as in particular an exhaust gas heatexchanger, having a fluid channel, such as a tube array, through which afirst medium, such as exhaust gas, can flow, and a second fluid channel,such as a housing, through which a second medium, such as a coolant, canflow, the ends of the tube array being connected to the tube plates, forexample in a cohesive manner, and the tube plates being connected to thehousing, for example in a cohesive manner, characterized in that thehousing has an expansion element.
 2. The heat exchanger as claimed inclaim 1, characterized in that a sealing element, such as a metalbellows, is arranged on the housing, covering and sealing the expansionelement.
 3. The heat exchanger as claimed in claim 1, characterized inthat the expansion element is formed in one piece with a sealingelement.
 4. The heat exchanger as claimed in claim 1, characterized inthat the expansion element is formed as at least one circumferentialbead or a plurality of circumferential beads.
 5. The heat exchanger asclaimed in claim 1, characterized in that the expansion element is atleast one region of the housing covered with slots.
 6. The heatexchanger as claimed in claim 1, characterized in that, as an expansionelement, the housing or a region of the housing has slots which runtransversely with respect to the longitudinal direction of the tubes andin the circumferential direction of the housing, which in each caseextend only over part of the circumference and which in thecircumferential direction partly overlap slots arranged axially offset.7. The heat exchanger as claimed in claim 1, characterized in that atleast one group of slots having at least two slots is provided in thehousing.
 8. The heat exchanger as claimed in claim 1, characterized inthat the at least one group of slots is arranged in a central region ofthe housing, as viewed in the longitudinal direction of the heatexchanger.
 9. The heat exchanger as claimed in claim 1, characterized inthat the at least one group of slots is arranged in an end region orclose to an end region of the housing, as viewed in the longitudinaldirection of the heat exchanger.
 10. The heat exchanger as claimed inclaim 1, characterized in that two groups of slots are provided.
 11. Theheat exchanger as claimed in claim 10, characterized in that the twogroups of slots are arranged in the two end regions or close to the endregions of the housing.
 12. The heat exchanger as claimed in claim 10,characterized in that the groups of slots has at least two or amultiplicity of slots, such as three, four, five, six, etc. slots. 13.The heat exchanger as claimed in claim 1, characterized in that fourslots are arranged in the housing or in a group of slots, in each casetwo extending over less than half the circumference in one of twotransverse planes and slotted regions of the other transverse planebeing located opposite the non-slotted regions of a transverse plane.14. The heat exchanger as claimed in claim 1, characterized in that,given an arrangement of two slots per group of slots, the slots arespaced apart and are formed in such a way that they run beside oneanother in a subregion of their extent and leave a narrow land betweenthemselves.
 15. The heat exchanger as claimed in claim 1, characterizedin that, given an arrangement of three slots per group of slots, theslots are spaced apart and are formed in such a way that they run besideone another in a subregion of their extent and leave two narrow landsbetween themselves.
 16. The heat exchanger as claimed in claim 1,characterized in that, given a group of slots, at least two lands or amultiplicity of lands, such as three, four, etc., are formed, as viewedover the circumference of the housing.
 17. The heat exchanger as claimedin claim 16, characterized in that, given a group of slots with anarrangement of two lands per group, the lands lie opposite one another,as viewed in the radial direction of the housing.
 18. The heat exchangeras claimed in claim 16, characterized in that, given a group of slotswith an arrangement of two or more lands per group, the lands aredistributed uniformly, as viewed in the circumferential direction of thehousing.
 19. The heat exchanger as claimed in claim 1, characterized inthat four lands are formed by four slots which partly intersect at fourpoints of the housing.
 20. The heat exchanger as claimed in claim 1,characterized in that four times two parallel lands are formed by sixslots which partly intersect at four points of the housing.
 21. The heatexchanger as claimed in claim 1, characterized in that the slots have ateardrop shape in their end regions.
 22. The heat exchanger as claimedin claim 1, characterized in that the slots are introduced into thehousing by means of one of the following processes: laser cutting, waterjet cutting, sawing, milling, erosion or punching.
 23. The heatexchanger as claimed in claim 1, characterized in that the expansionelement and/or the sealing element is formed from one of the followingmaterials: metal, steel, elastomer, silicone.
 24. The heat exchanger asclaimed in claim 1, characterized in that the expansion element and/orthe sealing element is connected to a housing part or two housing partsor is formed in one piece with the latter.
 25. The heat exchanger asclaimed in claim 1, characterized in that the expansion element and/orthe sealing element is connected to the housing by welding, soldering,by means of clamping elements or by means of adhesive bonding.